This invention relates to bases for cathode ray tubes, and more particularly relates to self-adhering bases which can be used both as an in-process base and a permanent base.
Cathode ray tubes, such as those used for color television and related display applications, have a glass envelope with a face panel portion including a phosphor screen, and a neck portion oriented normal to the face panel and containing an electron gun. In operation, the gun generates electron beams which are swept across the screen in a controlled manner to activate the phosphors and produce a display. These electron beams are generated, focused and accelerated toward the screen by means of a series of discrete components in the gun assembly, including at least one thermionic cathode and a series of electrodes. The beams are generated by the cathode, which is activated by a heater coil. The beams are then focused and accelerated toward the screen by the electrodes, each of which is held at a separate electrical potential chosen to create the desired effect on the beams generated by the cathode.
Because the interior of the tube is held at a vacuum, the electrical leads for the cathode heater and the electrodes are connected to base pins sealed in the glass bottom of the tube neck. The base pins are oriented in a circular array to mate with a socket in the television chassis. In order to provide both mechanical support and electrical insulation for these base pins, the bottom of the tube neck is fitted with a plastic base designed to mate both with the pins and the tube socket. This base typically has a circular basal or bottom portion with a series of pin apertures, an upstanding cylindrical portion called a "lug", and an upstanding shield portion connected to the lug and called a "silo". The basal portion supports a series of truncated cone-shaped walls surrounding the apertures and called "outer beads".
When the tube and base are assembled, the basal portion contacts the bottom of the tube neck and the pins extend through the basal apertures a sufficient distance to mate with the socket. The silo substantially surrounds one pin which is associated with a high voltage electrode, in order to provide arc-over protection for the pins. The silo has an open top to allow electrical connection of the high voltage pin with the socket. In order to provide adherence of the base to the tube, as well as additional electrical insulation between the pins, a bead of a room temperature curable silicone resin, such as silite 100 (a trademark of DEVCON CORP.), is typically applied to the bottom of the base in the pin area prior to assembly.
In the manufacture of cathode ray tubes, it has long been the practice to "process" the tubes after evacuation and sealing of the tube envelope and prior to insertion of the base. Such processing is also known as "high voltage conditioning" and is designed to remove small particles and projections, particularly from the gun assembly, where small inter-electrode spacings would otherwise be prone to high voltage arcing during later tube operation. Typically, specially designed process bases and sockets have been used for this purpose.
It has been recognized that considerable increases in manufacturing efficiencies could be realized by the development of a cathode ray tube base which could be used both as an in-process base during tube manufacture and as a permanent base during tube operation. A principal obstacle to the achievement of this goal has been the lack of either a suitable adhesive or a suitable self-adhering base. The time required for the curing of adhesives which are fully compatible with the manufacturing process is too long to allow the realization of required production speeds. Alternatively, reducing the size of the base apertures to create an adherence sufficient to withstand socket insertion and extraction forces during processing has led to other problems. For example, the normal variation in pin locations among production tubes creates stresses in both the neck and the base, resulting in bent pins, cracks in the neck bottom surrounding the glass-to-metal pin seals, and other problems.
A type of self-adhering base is known which replaces two normally shaped apertures with slot-shaped apertures smaller in width than the pins. The smaller width creates a force fit with the two mating pins, while the slot shape provides a certain amount of accommodation for variations in pin location. However, in practice it has been found that: (1) the adherence provided by the base is insufficient to withstand the normal socket insertion and extraction forces encountered during tube processing; and (2) the slot shaped apertures do not reduce the stresses sufficiently to avoid the pin problems referred to above.
Accordingly, it is an object of the invention to provide a self-adhering base for a cathode ray tube which substantially avoids the above problems while providing sufficient adherence to the tube pins to allow use of the base both as an in-process base and a permanent base.
It is a further object of the invention to provide a self-adhering base for a cathode ray tube which is easily manufacturable, and compatible both with present cathode ray tube designs and cathode ray tube manufacturing processes.
In accordance with the invention, there is provided a cathode ray tube base having: a bottom or basal portion defining an array of apertures for mating with an array of cathode ray tube pins extending from the bottom of the neck of the tube, each aperture surrounded by a wall or bead upstanding from the basal portion; the base also having: a cylindrical portion upstanding from the central portion of the basal portion; the base may also have an open-topped shield portion surrounding at least one of the pin apertures and its associated bead, for shielding a high voltage pin.
In accordance with the self-adhering aspects of the base, a first one of the apertures has a smaller opening than that of its associated pin, preferably a shielded aperture, and two other of the apertures are slot-shaped, the three apertures located approximately equidistantly from one another, and the two slot-shaped apertures oriented to have their long axes intersect the approximate location of the first aperture. Slots are oriented in a direction to relieve the direction of stress at the stem leads.
In accordance with a preferred embodiment, the apertures are distributed in a circular array and the long axes of the slots form an angle with a line bisecting both the first aperture and the array, the angle within the range of about 20 to 30 degrees.
In accordance with another preferred embodiment, the side walls of the slot-shaped apertures each have a planar portion and a concave conical portion, the ratio of the slot width to its associated pin width is within the range of about 0.37 to 0.51, which ratios have been found to result in optimum pin retention force without undue stress on either the base, the pins, or the glass-to-metal pin seal in the neck.